(a) Field of the Invention
The present invention relates to a valve system, more particularly, the variable valve system equipped with a variable tappet.
(b) Description of the Related Art
Generally, technical developments are ongoing in a variety of fields of the vehicle industry. Among them, a field for improving fuel efficiency of an engine is important in aspects of environment and energy saving.
An engine having CDA (cylinder de-activation) improves fuel efficiency by stopping function of some cylinders in an idle or low load driving condition.
FIGS. 1A and 1B show operating states of a valve system equipped with a general variable tappet.
As shown, the valve system is equipped with a variable tappet. The variable tappet is provided on an upper end portion of a stem 1a of a valve.
The variable tappet includes an inner tappet 3, an outer tappet 5, and a locking pin 7. First cams 13 and a second cam 11 are formed on a camshaft 9.
The first cams 13 correspond to the outer tappet 5, and the second cam 11 corresponds to the inner tappet 3.
The inner tappet 3 and the outer tappet 5 move together by the locking pin 7 as the locking pin 7 couples the outer tappet 5 and the inner tappet 3, referring to FIG. 1A. The stem 1a is moved by the first cams 13.
The inner tappet 3 and the outer tappet 5 may move separately, as the locking pin 7 is disengaged from the inner tappet 3, referring to FIG. 1B. The stem 1a is moved by the shorter second cam 11. Further, the outer tappet 5 compresses a lost spring 1b, so a movement of the stem 1a is restricted.
The locking pin 7 is operated by hydraulic pressure.
However, a movement of the valve by the first cam 13 is controlled by a movement of the outer tappet 5, so there is a problem in that the overall length (L) of the variable tappets 3 and 5 is increased.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.